Photomask producing method and photomask blank

ABSTRACT

In a photomask blank serving as a base member for producing a halftone-type phase shift mask in which a light-transmissive substrate is formed thereon with a light-semitransmissive phase shift pattern having a desired opening, a light-semitransmissive phase shift film, a chromium film, and an etching mask film are stacked in order on the light-transmissive substrate. The etching mask film is made of an inorganic-based material having a resistance against dry etching of the chromium film. The photomask blank further may has a resist film formed on the etching mask film.

This is a divisional of application Ser. No. 11/949,566 filed Dec. 3,2007, which is a divisional of application Ser. No. 10/820,785 filedApr. 9, 2004. The entire disclosure(s) of the prior application(s),application Ser. Nos. 11/949,566 and 10/820,785 are considered part ofthe disclosure of the accompanying divisional application and is herebyincorporated by reference.

This application claims priority to Japanese Patent Application No.2003-105921, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to a method of producing a photomask for use inproduction of a semiconductor integrated circuit, a liquid crystaldisplay device, or the like, and to a photomask blank for use therein.

Following high integration of semiconductor integrated circuits, liquidcrystal display devices, etc., and so forth, there has been anincreasing demand for high pattern accuracy with respect to photomasksthat are used in fine processing during the production process thereof.

In the photomasks currently used, a pattern formed by an opaque film isprovided on a transparent substrate, and a chromium-based material isgenerally used as the opaque film in terms of processability of a highlyaccurate pattern.

However, with respect to the demand for higher accuracy of the patternsof the photomasks following the high integration of the semiconductorintegrated circuits and so forth, it has become clear that the currentmethod of forming a pattern from a chromium-based opaque film by using aresist pattern as an etching mask raises a problem of variation in CD(critical dimension) accuracy due to the loading effect in connectionwith a photomask wherein pattern regions having a global opening ratiodifference are compositely present in the mask plane. As the photomaskwherein the pattern regions having the global opening ratio differenceare compositely present in the mask plane, there is specifically cited aphotomask wherein a plurality of kinds of functional devices aredisposed in the mask plane. As such a photomask, there is cited, forexample, a photomask having patterns with a difference in density andused in production of a system LSI wherein memories, logic circuits, andso forth are compositely mounted, or a D-RAM, a liquid crystal displaydevice, or the like wherein memory cells or pixel regions, andperipheral circuits and so forth formed therearound are compositelymounted. In such a photomask, for example, the opening ratios of opaquepatterns (the ratios of portions where no opaque films are formed)differ between a memory region and a logic circuit region. In thecurrent state, in order to produce such a photomask, a desired resistpattern is first formed on a chromium-based opaque film, then, usingthis resist pattern as a mask, the chromium-based opaque film ispatterned by dry etching mainly with radicals by the use of achlorine-based and oxygen-based mixture gas or the like. For example,when resist patterns having the same dimensions are formed in respectiveregions having an opening ratio difference in opaque pattern so as toform chromium-based opaque film patterns of the same dimensions,respectively, there arises a problem that the respective opaque patternsformed by dry etching using the resist patterns of the same dimensionsas masks exhibit different dimensions due to the difference between theopening ratios in the respective regions by the so-called loading effectto thereby cause variation in CD accuracy.

Here, the loading effect is a phenomenon that etching characteristics(etching rate, selection ratio, etc.) change depending on a magnitude ofan etching area of an etching-subject film so that a CD shift in themask plane changes (see, e.g. VSLI Synthetic Dictionary (Science Forum)pp. 865). More specifically, it is a phenomenon that when the etchingarea increases, the utilization efficiency of etchants decreases toreduce the etching rate (see, e.g. Submicron Lithography “SyntheticTechnological Material Collection” pp. 353).

Generally, in dry etching of a thin film made of a material containingchromium, chlorine and oxygen are used as dry etching gases to etchchromium by producing chromyl chloride. There is a problem that sincecontribution of radicals is large in this etching reaction, the etchingprogress directivity is particularly difficult to control.

As a means for solving the problem about the photomask caused by thereduction in CD accuracy due to the foregoing loading effect, there is amethod wherein a pattern accuracy in etching is not lowered by improvinginequality of opening ratios in a pattern peripheral region and apattern central portion (see, e.g. Japanese Patent ApplicationPublication (JP-A) No. 2001-183809). Specifically, this method is amethod of providing a peripheral opening ratio adjusting pattern in anon-irradiated region where light from a light source is not irradiatedin an exposure process using a photomask.

On the other hand, there is also a method of disposing a dummy etchingpattern for dry etching rate correction in a pattern exposure region oroutside the pattern exposure region when producing a phase shiftphotomask (see, e.g. Japanese Patent Application Publication (JP-A) No.H8-234410). In this method, as the dummy etching pattern in the patternexposure region, use is made of a pattern having a size not greater thanthe resolution limit by transfer.

However, in the conventional methods described in Japanese PatentApplication Publication (JP-A) No. 2001-183809 and Japanese PatentApplication Publication (JP-A) No. H8-234410, there is a problem thatwhen local inequality exists in the pattern opening ratio (i.e. whenpattern regions with different densities compositely exist), it iscomplicated to provide an adjusting pattern corresponding thereto and itis difficult to cope with high integration of semiconductor integratedcircuits. Further, since it is necessary to form the pattern that is notnormally required, an increase in pattern data amount used in productionof a photomask can not be avoided. This becomes a large problem inproducing semiconductor devices with extremely high integration inrecent years.

As a literature describing another method of suppressing the loadingeffect, there is U.S. Pat. No. 6,472,107. This literature describes thatthe loading effect can be suppressed by etching an opaque film by theuse of a hard mask layer made of Ti, TiW, W, Si₃N₄, SiO₂, TiN, spin-onglass, or the like. In this method, it is not necessary to form thepattern, which is not normally required, when producing the photomasklike in Japanese Patent Application Publication (JP-A) No. 2001-183809and Japanese Patent Application Publication (JP-A) No. H8-234410 asdescribed above. Note that the method itself of etching the opaque filmby the use of the hard mask layer as described in U.S. Pat. No.6,472,107 has been proposed for a long time also as a technique ofsolving a problem of reduction in CD accuracy when use is made of aresist having a small dry etching resistance (see, e.g. Japanese PatentPublication (JP-B) No. S63-39892). In terms of improving the CDaccuracy, as another technique of improving the CD accuracy of achromium film pattern, Japanese Patent Application Publication (JP-A)No. H10-69055, for example, discloses that the CD accuracy is improvedby reducing the thickness of a chromium film and the thickness of aresist film that requires about three times the thickness of thechromium film.

Meanwhile, there is a phase shift mask as a photomask apart from the onecalled a binary mask and having been used for a long time wherein theopaque film pattern is formed on the transparent substrate. The phaseshift mask improves contrast of a transferred image by providing a phaseshifter portion on the mask and by shifting by 180° the phase of lightpassing through the phase shifter portion and a portion adjacent theretoto cause mutual interference of the light at a boundary portiontherebetween. As the kind of phase shift mask, there are cited, forexample, a Levenson type, a halftone type, a chromeless type, and soforth. A phase shifter layer in the Levenson-type phase shift mask isformed by normally etching a glass or is comprised of a film made of amaterial serving to shift a phase. A phase shifter layer in thehalftone-type phase shift mask is comprised of a semitransparent phaseshift material layer. These phase shift masks require an opaque ring ata peripheral portion of a pattern region for preventing leakage ofexposure light. A chromium-based opaque film is normally used as thisopaque ring. In the production of a phase shift mask having such anopaque ring, use is normally made of a blank in which an opaque film isformed on a phase shift material layer. First, the opaque film is etchedto form a desired opaque film pattern, then the phase shift materiallayer is etched using the opaque film pattern as an etching mask for thephase shift layer, and then the opaque film is removed while leaving atleast a portion of the opaque film that will serve as the opaque ring,thereby to produce the phase shift mask. By using such a method, thephase shift material layer has achieved a higher CD accuracy as comparedto etching using a resist pattern as a mask.

Meanwhile, in recent years, further integration of the semiconductordevices has been advanced, wherein the line width has also beendiscussed from a line width of up to 130 nm to a line width of 90 nm, 65nm, and further 45 nm so that higher densification of patterns has alsobeen advanced. Therefore, there is a tendency that patterns of thephotomasks are also formed further finer and much stricter values arerequired also for the CD accuracy thereof. There is also a tendency thatsince diversification of the patterns has been advanced, differences indensity of the patterns also increase.

As described above, the foregoing U.S. Pat. No. 6,472,107 describes thatthe loading effect is suppressed by using the hard mask, and JapanesePatent Publication (JP-B) No. S63-39892 describes about improving the CDaccuracy by using the hard mask. However, in order to suppress theloading effect and to achieve the high CD accuracy under thecircumstances where the finer formation of the patterns and thedifferences in density of the patterns are in progress as describedabove, it is insufficient to merely use the hard mask and furthertechnological improvement is required.

On the other hand, in terms of the improvement in CD accuracy under theforegoing circumstances, in the method described in Japanese PatentApplication Publication (JP-A) No. H10-69055, since the chromium-basedopaque film requires a prescribed opaque property (e.g. OD (opticaldensity) of 3.0 or more), there is a limit to reduction in thickness ofthe opaque film, and resultantly, there is also a limit to reduction inthickness of the resist, and therefore, there is a limit to improvementin CD accuracy.

Further, in the production of the phase shift mask, the pattern shape ofthe opaque film to serve as the etching mask is directly reflected onthe pattern shape of the phase shift material layer, and therefore, adimension control of the opaque film pattern performs a very importantrole. In particular, the phase shift mask is a mask that is effective infine formation of a pattern in a semiconductor device as compared to thebinary mask. In recent years, since further finer formation of patternshas been progressed, further stricter dimensional accuracy of phaseshift material layers has been required. On the other hand, there isalso a problem that, depending on the etching condition of the phaseshift material layer, the surface of the chromium-based opaque film isdamaged on etching of the phase shift material layer, and particlesgenerated thereby affect the etching of the phase shift material layerand remain as a pattern defect, which thus narrows the width ofselection in etching condition.

SUMMARY OF THE INVENTION

This invention has been made for solving the foregoing problems.

Specifically, a first object of this invention is to provide a methodthat can suppress the loading effect and achieve a high CD accuracy whenforming a highly accurate pattern by dry etching, in a photomask havinga global opening ratio difference (variation in CD accuracy due to theloading effect becomes a problem).

Further, a second object of this invention is to provide a method ofproducing a photomask, which can form a pattern having a high CDaccuracy regardless of the foregoing regions (over the whole surface ofthe mask) having a global opening ratio difference (variation in CDaccuracy due to the loading effect becomes a problem) in the mask plane,and a photomask blank for use in the method.

Moreover, a third object of this invention is to provide a method thatcan suppress the loading effect and achieve a high CD accuracy onetching an opaque film as an etching mask layer when producing ahalftone-type phase shift mask or a chromeless-type phase shift maskcomprising a phase shift layer having a global opening ratio difference(variation in CD accuracy due to the loading effect becomes a problem).

According to a first aspect of this invention, there is obtained amethod of producing a photomask in which a light-transmissive substrateis formed thereon with a chromium pattern having a global opening ratiodifference in its plane on the light-transmissive substrate, the methodcharacterized by comprising the steps of preparing a photomask blankhaving, on the light-transmissive substrate, at least a chromium filmfor forming the chromium pattern, an etching mask film made of aninorganic-based material having a resistance against etching of thechromium film, and a resist film; of exposing and developing the resistfilm with a desired pattern to form a resist pattern; of applying dryetching to the etching mask film using the resist pattern as a mask toform an etching mask pattern; and of applying dry etching to thechromium film using the etching mask pattern as a mask to form thechromium pattern, wherein the dry etching of the chromium film iscarried out under a condition selected from conditions that cause damageto the resist pattern to a degree which is unallowable when etching thechromium film using the resist pattern as a mask.

In the foregoing photomask producing method according to the firstaspect of this invention, it is preferable that the condition thatcauses damage to the resist pattern which is unallowable when etchingthe chromium film using the resist pattern as a mask be a condition thatincreases anisotropy of dry etching and/or a condition that increases anetchant density of etching. Further, the photomask may be a binary maskhaving the chromium pattern on the light-transmissive substrate. It maybe configured to further include a step of stripping the etching maskpattern after forming the chromium pattern. Further, the etching maskpattern may be left on the chromium pattern as a film having areflection preventing function. The photomask may be a phase shift maskand the photomask blank may have a phase shift film between thelight-transmissive substrate and the chromium film, and it may beconfigured to further include a step of forming the phase shift patternusing the chromium pattern as a mask after the step of forming thechromium pattern. The photomask may be a phase shift mask and it may beconfigured to include a step of patterning the light-transmissivesubstrate to form a phase shift groove using the chromium pattern as amask after the step of forming the chromium pattern.

According to a second aspect of this invention, there is obtained aphotomask producing method of producing a halftone-type phase shift maskin which a light-transmissive substrate is formed thereon with alight-semitransmissive phase shift film pattern having a global openingratio difference in its plane on the light-transmissive substrate, themethod characterized by comprising the steps of preparing a photomaskblank having, on the light-transmissive substrate, at least alight-semitransmissive phase shift film for forming thelight-semitransmissive phase shift film pattern, a chromium film forforming the chromium pattern, an etching mask film made of aninorganic-based material having a resistance against etching of thechromium film, and a resist film; of exposing and developing the resistfilm with a desired pattern to form a resist pattern; of applying dryetching to the etching mask film using the resist pattern as a mask toform an etching mask pattern; of applying dry etching to the chromiumfilm using the etching mask pattern as a mask to form the chromiumpattern; of applying dry etching to the light-semitransmissive phaseshift film using the chromium pattern as a mask to form alight-semitransmissive phase shift film pattern; and of removing adesired part or the whole of the chromium film pattern.

In the foregoing photomask producing method according to the secondaspect of this invention, the etching mask pattern may be stripped withthe dry etching of the light-semitransmissive phase shift film. Theetching mask pattern may be left on the chromium pattern as a filmhaving a reflection preventing function. The light-semitransmissivephase shift film may include an uppermost layer made of a materialcontaining silicon, and nitrogen and/or oxygen. Thelight-semitransmissive phase shift film may be a film of a monolayerstructure made of a material containing metal, silicon, and nitrogenand/or oxygen.

According to a third aspect of this invention, there is obtained aphotomask producing method of producing a chromeless-type phase shiftmask in which a light-transmissive substrate is formed thereon with alight-transmissive phase shift pattern having a global opening ratiodifference in its plane on the light-transmissive substrate, the methodcharacterized by comprising the steps of preparing a photomask blankhaving, on the light-transmissive substrate, at least a chromium filmfor forming the chromium pattern, an etching mask film made of aninorganic-based material having a resistance against etching of thechromium film, and a resist film; of exposing and developing the resistfilm with a desired pattern to form a resist pattern; of applying dryetching to the etching mask film using the resist pattern as a mask toform an etching mask pattern; of applying dry etching to the chromiumfilm using the etching mask pattern as a mask to form the chromiumpattern; of applying dry etching to the light-transmissive substrateusing the chromium pattern as a mask to form the light-transmissivephase shift pattern; and of removing a desired part or the whole of thechromium pattern.

In the foregoing photomask producing method according to the thirdaspect of this invention, the etching mask pattern may be stripped withthe dry etching of the light-transmissive substrate. Further, theetching mask pattern may be left on the chromium pattern as a filmhaving a reflection preventing function.

In the foregoing photomask producing methods according to the first tothird aspects of this invention, it may be configured to include a stepof stripping, before the step of forming the chromium pattern, theresist pattern remaining in the step of forming the etching maskpattern. It is preferable that the etching mask film made of theinorganic-based material be made of a material containing at least oneof molybdenum, silicon, tantalum, and tungsten. It is preferable that,in the step of forming the chromium pattern, an etching rate of thechromium film be ten or more times an etching rate of the etching maskpattern.

According to a fourth aspect of this invention, there is obtained aphotomask blank serving as a base member for producing a halftone-typephase shift mask in which a light-transmissive substrate is formedthereon with a light-semitransmissive phase shift film pattern having adesired opening, the photomask blank characterized in that alight-semitransmissive phase shift film, a chromium film, and an etchingmask film made of an inorganic-based material having a resistanceagainst dry etching of the chromium film are laminated in order on thelight-transmissive substrate.

In the foregoing photomask blank according to the fourth aspect of thisinvention, the light-semitransmissive phase shift film may include anuppermost layer made of a material containing silicon, and nitrogenand/or oxygen. The light-semitransmissive phase shift film may be a filmof a monolayer structure made of a material containing metal, silicon,and nitrogen and/or oxygen. The etching mask film may be made of amaterial that is possible to strip with the dry etching of thelight-semitransmissive phase shift film. The etching mask film may be afilm having a reflection preventing function.

In this invention, as the etching mask for the chromium film, use ismade of the etching mask pattern made of the inorganic-based materialhaving a resistance against the etching of the chromium film.

Dry etching is normally carried out by producing ions and radicals andreacting these etchants with an etching object. Generally, it isconsidered that, in dry etching of a chromium film using a mixture gasof chlorine-based gas (e.g. Cl₂) and oxygen-based gas (e.g. O₂) as a dryetching gas, the reaction occurs mainly with the action of radicals. Thedry etching mainly with radicals is defined as a method of controllablyproducing more radicals than ions as etchants and of reacting them withan etching object. In dry etching of a chromium film, it is consideredthat when producing a mask having a global opening ratio difference inthe mask plane, the loading effect is generated due to an etching areadifference of the chromium film and a coating ratio difference of aresist pattern, caused by consumption of oxygen radicals due toisotropic etching of a resist caused by isotropic etching componentsbeing radicals, oxygen radicals, etc., and so forth. On the other hand,when etching of a chromium film is carried out using as a mask anetching mask pattern made of an inorganic-based material, if use is madeas the etching mask pattern of a pattern with less influence of theloading effect and less variation in CD accuracy as compared to achromium film pattern formed by dry etching under the optimum condition,a chromium film pattern transferred with such a pattern shape can be onewith less influence of the loading effect and less variation in CDaccuracy as compared to the conventional one. In order to obtain such anetching mask pattern, there are cited, for example, the following threemethods.

As the first method, there is cited a method where, in selection of amaterial of an inorganic-based etching mask pattern (inorganic-basedetching mask layer) and a kind and a condition of a dry etching gas,such a combination is selected that enables dry etching where thereaction occurs mainly with the action of ions. The dry etching mainlywith ions is defined as a method of controllably producing more ionsthan radicals as etchants and of reacting them with an etching object.In the dry etching mainly with ions, anisotropic etching tends to becarried out as compared to the dry etching mainly with radicals, andtherefore, it is possible to reduce a CD shift of a pattern in theetching. Further, the dry etching mainly with ions is etching whereanisotropic etching components are major and a pattern with an excellentsectional shape tends to be formed. As a gas to be used in such dryetching mainly with ions, use can be made of, for example, afluorine-based gas such as SF₆, CF₄, C₂F₆, or CHF₃, or a mixture gasthereof with He, H₂, N₂, Ar, C₂H₄, or O₂, or a chlorine-based gas suchas Cl₂ or CH₂Cl₂, or a mixture gas thereof with He, H₂, N₂, Ar, or C₂H₄.

As the second method, there is cited a method where, in selection of amaterial of an inorganic-based etching mask pattern (inorganic-basedetching mask film) and a kind and a condition of a dry etching gas, theetching selection ratio relative to the resist film (etching rate ofinorganic-based etching mask pattern material/etching rate of resist) isset greater than the etching selection ratio between a chromium filmpattern (chromium film) and the resist film under the optimum etchingcondition of the chromium film. By increasing the foregoing selectionratio, it becomes possible to reduce a CD shift of the pattern in theetching. In this case, it is preferable that (etching rate ofinorganic-based etching mask pattern material/etching rate of resist) betwo or more.

As the third method, there is cited a method where the thickness of anetching mask pattern is set smaller than the thickness of a chromiumfilm. Since the chromium film is basically etched using an etching maskpattern as a mask, it is not necessary to take into account thethickness of a resist pattern necessary for etching the chromium film.As a result, by forming the etching mask pattern as a thinner film, itbecomes possible to reduce the thickness of the resist necessary foretching thereof so that the etching mask pattern with high resolutioncan be obtained. That is, when the resist pattern is thin, the resistpattern having a more excellent pattern sectional shape can be formed sothat the CD accuracy of the etching mask pattern formed by the use ofsuch a resist pattern is also improved. Further, as described above, dryetching for the chromium pattern can basically be carried out using onlythe etching mask pattern, and therefore, etching of the chromium filmcan be carried out in the presence of a small amount of the resist, i.e.only the residual pattern of the thin resist, or in the state of noresist by performing a resist stripping process. Accordingly, it ispossible to further reduce the loading effect that is considered to becaused by consumption of oxygen radicals by the resist pattern. In thiscase, the thickness of the etching mask layer is preferably set to 5 to30 nm.

Note that the foregoing first to third methods may be adopted one by oneor in combination thereof simultaneously.

As described above, in this invention, dry etching is applied to thechromium film using as a mask the etching mask pattern having a patternwith less influence of the loading effect and excellent in CD accuracyvariation. Therefore, as compared to the conventional technique using asa mask the resist pattern of which the pattern shape is deterioratedduring dry etching of the chromium film, the pattern accuracy (CDaccuracy and its variation) of the chromium pattern is significantlyimproved.

Further, in this invention, dry etching of the chromium film is carriedout under a condition selected from conditions that cause damage to theresist pattern to a degree which is unallowable when etching thechromium film using the resist pattern as a mask. As the condition thatcauses large damage to the resist pattern, there is cited a conditionwhere etching anisotropy is high. As described above, although etchingof the chromium film is etching mainly with radicals considered to beisotropic etching components, it is possible to increase ionicity bycontrolling the dry etching condition, and to resultantly increase theanisotropy. Since increasing the anisotropy is the condition thatfacilitates giving damage to the resist pattern, it can not be employedin the conventional etching of the chromium film using the resistpattern as a mask. However, in this invention, since the etching maskpattern serves as a mask, it is not necessary to take into accountdamage to the resist pattern so that such a condition can be adopted.Even when increasing the anisotropy not only causes an increase inperpendicularity of the pattern sectional shape, but also causesoccurrence of variation in etching rate in the mask plane due to someloading effect, since side etching of the pattern is reluctant toprogress, variation in CD shift in the plane is reduced. Further, sincethe side etching amount of the pattern is small also relative to overetching that is carried out for making perpendicular the sectional shapeof the chromium film pattern, the CD shift of the pattern due to theover etching can be much more controlled as compared to the conventionaltechnique.

Furthermore, as the condition that causes large damage to the resistpattern, there is cited a condition that increases the density ofetchants. As a method of decreasing the loading effect, there isconsidered a method of keeping constant the utilization efficiency ofthe etchants in the plane by adopting a dry etching condition thatincreases the density of the etchants. However, since this conditionalso facilitates giving damage to the resist pattern, it can not beemployed in the conventional etching of the chromium film using theresist pattern as a mask. Particularly, such a dry etching conditionthat increases the density of the etchants under the condition where theanisotropy is increased is never employed because damage to the resistpattern is remarkably caused. In this invention, since the etching maskpattern serves as a mask, it is not necessary to take into accountdamage to the resist pattern so that such a condition can be employed.

As described above, in this invention, it is made possible to adopt thedry etching condition of the chromium film that suppresses the loadingeffect to improve the CD accuracy, which can not be adoptedconventionally. Consequently, it becomes possible to broaden the widthof controllability of the dry etching condition of the chromium film.

Note that, in the dry etching of the chromium film, the condition ofhigh anisotropy can be achieved by using the condition that increasesthe ionicity in the dry etching mainly with radicals. The condition thatincreases the ionicity is preferably the condition where the ionicity isincreased to a level where ions and radicals are approximately equal toeach other.

In the dry etching in this invention, as a control method of theetchants when implementing the dry etching mainly with radicals wherethe ionicity is increased, there is cited a method of controllingvarious dry etching conditions (e.g. pressure in a chamber, gas flowrate, and RF power). That is, the dry etching mainly with ions orradicals is not determined based on a kind of gas, but, even when thesame kind of gas is used, it is possible to carry out both the dryetching mainly with ions and the dry etching mainly with radicals bycontrolling the dry etching conditions. Further, as a method ofincreasing the density of the etchants, there can also be cited themethod of controlling various dry etching conditions (e.g. pressure in achamber, gas flow rate, and RF power).

In this invention, the thickness of the resist film depends on arelationship with the foregoing inorganic-based etching mask layer inthe dry etching, and compositions and thicknesses of the foregoinginorganic-based etching mask layer and the foregoing opaque film may betaken into account. The resist film requires a thickness such that theresist film remains at least until completion of etching (including overetching) of the inorganic-based etching mask layer or thereafter. Thethickness of the resist film may be set such that the resist filmremains until completion of etching (including over etching) of theopaque film. Specifically, it is preferably 50 nm to 500 nm.

The resist pattern may be removed before forming the chromium filmpattern. In this case, the chromium film pattern is formed using onlythe inorganic-based etching mask pattern as a mask.

In the dry etching mainly with radicals, the etching selection ratio ofthe chromium film relative to the inorganic-based etching mask patternmaterial is preferably ten or more times (the etching rate of the opaquefilm is ten or more times the etching rate of the inorganic-basedetching mask pattern material). The thickness of the inorganic-basedetching mask pattern depends on the thickness of the chromium film interms of a relationship with dry etching of the chromium film, and theinorganic-based etching mask pattern requires a thickness such that theinorganic-based etching mask pattern remains until completion of etching(including over etching) of the chromium film or thereafter.Specifically, it is preferably 5 nm to 100 nm and, when reduction inthickness of the etching mask is taken into account, it is preferablyset to 5 to 30 nm.

The inorganic-based etching mask pattern may be removed by a method suchas dry etching or wet etching after forming the chromium film pattern.On the other hand, when the inorganic-based etching mask layer is formedwith a composition and a thickness that exhibit the reflectionpreventing effect, it is possible to use the inorganic-based etchingmask pattern as a reflection preventing film without removing it. Withthis configuration, influence of multiple reflection in a projectionsystem caused upon exposure can be effectively suppressed.

On the other hand, a reflection preventing film may be formed betweenthe light-transmissive substrate and the opaque film. With thisconfiguration, influence of multiple reflection in an illuminationsystem caused upon exposure can be effectively suppressed. In this case,it is preferable in that the process of removing the inorganic-basedetching mask pattern becomes unnecessary.

In this invention, the opaque film is configured to have a compositionand a thickness so as to exhibit a prescribed opaque effect againstexposure light, for example, exposure light obtained by a KrF excimerlaser, an ArF excimer laser, or an F₂ excimer laser. Herein, thewavelength of the KrF excimer laser is about 248 nm, the wavelength ofthe ArF excimer laser is about 193 nm, and the wavelength of the F₂excimer laser is about 157 nm.

In this invention, the opaque film may be either a film of a uniformcomposition or a graded composition film with successive compositionmodulation in a direction of the thickness.

The chromium film represents a film mainly made of chromium. Thechromium film is not limited to a film of Cr alone, but includes asingle layer, a plurality of layers, a graded composition film, or thelike of CrO (representing inclusion of chromium and oxygen, and notspecifying the contents thereof, which shall apply hereinafter), CrN,CrC, CrCO, CrCN, CrON, CrCON, or the like.

As a dry etching gas used in etching the chromium film, ahalogen-containing gas and an oxygen-containing gas are normally used.As the halogen-containing gas, Cl₂ is the most popular and there arecited SiCl₄, HCl, CCl₄, CHCl₃, and so forth. Besides, use can be made ofa gas containing bromine or iodine. On the other hand, as theoxygen-containing gas, O₂ is the most popular, but CO₂, CO, or the likemay also be used.

In the photomask producing methods having the foregoing respectiveconfigurations, forming methods of various kinds of films are notlimited. The films can be formed by the use of sputtering apparatuses ofan in-line type, a single-wafer type, a batch type, and so forth. It is,of course, possible to form all the films on the light-transmissivesubstrate by the use of the same apparatus or a combination of aplurality of apparatuses.

Further, there is provided a method of producing a photomask wherein theinorganic-based etching mask pattern (inorganic-based etching masklayer) is made of a material containing at least one of molybdenum,silicon, tantalum, and tungsten.

As a material of the inorganic-based etching mask pattern, there iscited, for example, Mo alone, MoSi, MoSiO, MoSiN, MoSiON, Si alone, SiO,SiN, SiON, Ta alone, TaB, W, WSi, TaSi, or amorphous carbon.

This invention is not limited to the method of producing the binary maskin which the opaque chromium pattern is formed on the light-transmissivesubstrate, but is also applicable to the method of producing the phaseshift mask having the phase shift pattern formed by etching using thechromium pattern as a mask.

As the phase shift mask, there is a halftone-type phase shift mask inwhich the phase shift layer is light-semitransmissive. As thehalftone-type phase shift mask, there is cited a monolayer type or amultilayer type.

In the monolayer-type halftone phase shift mask, a semitransparent phaseshift pattern is formed on a light-transmissive substrate. Aninorganic-based etching mask pattern can be used for forming a chromiumfilm pattern that is used as a mask when forming the semitransparentphase shift pattern. (Mode A)

On the other hand, in the multilayer-type halftone phase shift maskproducing method, a two-layer type phase shift mask, for example, can beproduced by configuring the inorganic-based etching mask pattern to havea composition and a thickness that exhibit a phase shift effect and byconfiguring the chromium film pattern to have a composition and athickness that exhibit a light-semitransmitting effect. (Mode B)

As another example of the two-layer type halftone phase shift mask,there is one in which a transparent substrate is formed thereon with asemitransparent phase shift pattern comprised of a phase shift layer anda thin chromium film. In the case of this example, an inorganic-basedetching mask pattern can be used when forming a thin chromium patternthat is used in forming a pattern of the lower-layer phase shift film.In this case, it is possible to select the inorganic-based etching maskpattern so as to have an opaque function and to partly remove theinorganic-based etching mask pattern so that it remains at portionswhere the opaque function is required. (Mode C)

In the multilayer-type halftone phase shift mask, the semitransparentphase shift pattern is of a multilayer structure and has a desiredtransmittance and phase difference through the whole multilayerstructure. As an example of the two-layer type, there is one in which alight-transmissive substrate is formed thereon with a semitransparentphase shift pattern comprised of a transmittance adjusting layer and aphase shift layer. In the case of this example, an inorganic-basedetching mask pattern can be used when forming a chromium pattern that isused in forming a pattern of the uppermost-layer phase shift layer.(Mode D)

Further, in this invention, it is also possible to produce a phase shiftmask of a so-called substrate etching type.

For example, it is possible to produce a so-called etching-type phaseshift mask by configuring the chromium film pattern so as to have acomposition and a thickness that exhibit a light-semitransmitting effectand by etching part or the whole of the appearing light-transmissivesubstrate so as to have a prescribed phase difference relative totransmitted light through the chromium pattern. (Mode E)

Further, as another example of the so-called substrate etching typephase shift mask, there is a so-called etching-type phase shift mask(Levenson mask) in which a chromium film pattern in a line and spacefashion appears on the surface and one side of an adjacentlight-transmissive substrate is etched so as to have a prescribed phasedifference relative to the other side thereof. An inorganic-basedetching mask pattern can be used when forming a chromium pattern that isused as a mask when etching the substrate. (Mode F).

Further, as another example of the phase shift mask, there is, forexample, a mask in which an opening pattern and an auxiliary patterntherearound are formed on a transparent substrate by the use of alight-semitransmissive chromium film pattern having a phase differenceof approximately zero, and the auxiliary pattern is etched on thesubstrate so as to have a phase difference of approximately 180°relative to the opening pattern. In this mask, an inorganic-basedetching mask pattern can be used for forming the chromium pattern thatis used as a mask in etching the substrate. In this case, it is possibleto select the inorganic-based etching mask pattern so as to have anopaque function and to partly remove the inorganic-based etching maskpattern so that it remains at portions where the opaque function isrequired. (Mode G)

Further, as another example of the phase shift mask, there is, forexample, a mask in which an opening pattern and an auxiliary patterntherearound are formed on a transparent substrate by the use of alight-semitransmissive phase shift film having a phase difference ofapproximately 180°, and the opening pattern is etched on the substrateso as to have a phase difference of approximately 180° relative to theauxiliary pattern. In this mask, an inorganic-based etching mask patterncan be used for forming a chromium pattern that is used as a mask inetching the light-semitransmissive phase shift film and/or thesubstrate. (Mode H)

Further, as another example of the phase shift mask, there is, forexample, a so-called chromeless-type phase shift mask in which alight-transmissive substrate is etched into a prescribed pattern shapeso as to have a prescribed phase difference. An inorganic-based etchingmask pattern can be used for forming a pattern of a chromium film thatis used as a mask when etching the substrate. (Mode I)

Note that the inorganic-based etching mask pattern may be left as areflection preventing film in the foregoing Modes A, D, E, F, H, and I.

Particularly, in the halftone-type phase shift mask and thechromeless-type phase shift mask, the use of the inorganic-based etchingmask achieves reduction in loading effect, and further, theinorganic-based etching mask functions as a protective layer for thechromium film when etching the phase shift layer or the substrate.Therefore, damage to the surface of the chromium film is decreased sothat it is possible to remarkably diminish the problem that particlesgenerated thereby are transferred due to etching of the phase shiftmaterial layer and remain as a pattern defect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for describing photomask producing methods accordingto first and second embodiments of this invention.

FIG. 2 is an exemplary diagram of a resist pattern formed in theembodiments.

FIG. 3 is a diagram for describing photomask producing methods accordingto third and fourth embodiments of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of this invention will be described with reference to thedrawings. This invention, however, is not limited to these embodiments.

First Embodiment

Referring to FIG. 1, description will be made of a photomask producingmethod according to the first embodiment of this invention.

First, a substrate made of quartz was mirror-polished and was subjectedto prescribed washing to thereby obtain a light-transmissive substrate 1of 6 inches×6 inches×0.25 inches.

Then, by the use of an in-line sputtering apparatus where a plurality ofchromium (Cr) targets were disposed in the same chamber, an opaquechromium film 2 was formed on the light-transmissive substrate 1 (seeFIG. 1( a)).

Specifically, first, reactive sputtering was carried out in anatmosphere of mixture gas of argon (Ar) and nitrogen (N₂) (Ar:N₂=72:28[volume %], pressure 0.3 [Pa]) to thereby form a CrN film having athickness of 20 [nm].

Subsequently, reactive sputtering was carried out in an atmosphere ofmixture gas of argon (Ar) and methane (CH₄) (Ar:CH₄=96.5:3.5 [volume %],pressure 0.3 [Pa]) to thereby form a CrC film having a thickness of 37[nm] on the CrN film.

Subsequently, reactive sputtering was carried out in an atmosphere ofmixture gas of argon (Ar) and nitrogen monoxide (NO) (Ar:NO=87.5:12.5[volume %], pressure 0.3 [Pa]) to thereby form a CrON film having athickness of 15 [nm] on the CrN film.

The foregoing CrN film, CrC film, and CrON film were successively formedby the use of the in-line sputtering apparatus so that the opaquechromium film 2 containing these CrN, CrC, and CrON was configured suchthat these components continuously changed in a thickness directionthereof.

Then, by the use of a mixture target of molybdenum (Mo) and silicon (Si)(Mo:Si=20:80 [mol %]), reactive sputtering was carried out in anatmosphere of mixture gas of argon (Ar) and nitrogen (N₂) (Ar:N₂=10:90[volume %], pressure 0.3 [Pa]) to thereby form an MoSiN-basedinorganic-based etching mask film 3 having a thickness of 92 [nm] on theopaque chromium film 2 (see FIG. 1( b)).

Then, a positive electron beam resist 4 (ZEP7000: produced by ZeonCorporation) was applied on the inorganic-based etching mask film 3 tohave a thickness of 400 [nm] by the spin coat method (see FIG. 1( c)).

By the foregoing, preparation was made of a photomask blank 11 in whichthe opaque chromium film 2, the MoSiN-based inorganic-based etching maskfilm 3, and the resist 4 were formed in order on the light-transmissivesubstrate 1.

Then, the resist 4 was subjected to electron-beam drawing by the use ofJBX9000 produced by JEOL Ltd. and was then developed to thereby form aresist pattern 41 (0.4 μm line and space) as shown in FIG. 2 (see FIG.1( d)).

The formed resist pattern 41 has in the plane thereof a portion A and aportion B formed by the same pattern. In a region with a prescribed areaincluding the portion A, the resist around the portion A is not removedbut remains on the surface, while, in a region (white portion in thefigure) with the same prescribed area including the portion B, theresist around the portion B is removed so that the inorganic-basedetching mask film 3 appears on the surface. That is, by comparingpatterns at the portions A and B, it is possible to evaluate a CDcharacteristic obtained when pattern regions having a global openingratio difference are compositely present in the plane of a mask.

Then, dimensions of the obtained resist pattern 41 were measured at theportions A and B, respectively, by the use of CD-SEM (EMU-220) producedby Holon Inc.

Then, using the resist pattern 41 as a mask, dry etching mainly withionicity was carried out under a pressure of 5 [mmTorr] by the use of amixture gas of SF₆ and He to etch the inorganic-based etching mask film3 to thereby form an inorganic-based etching mask pattern 31 (see FIG.1( e)).

Then, using the resist pattern 41 and the inorganic-based etching maskpattern 31 as masks, dry etching mainly with radicals where ionicity wasincreased as much as possible (=ionicity was increased to a level whereions and radicals became approximately equal to each other) was carriedout under a pressure of 3 mmTorr by the use of a mixture gas of Cl₂ andO₂ to etch the opaque chromium film 2 to thereby form an opaque chromiumpattern 21 (see FIG. 1( f)).

Then, the resist pattern 41 and the inorganic-based etching mask pattern31 were stripped, and thereafter, prescribed washing was carried out toobtain a photomask 10 (see FIG. 1( g)).

Then, like the resist pattern 41, dimensions of the obtained opaquechromium pattern 21 were measured at the portions A and B, respectively,by the use of CD-SEM. As a result, a difference between size conversiondifferences (size differences each between the resist pattern 41 and theopaque chromium pattern 21) in the portions A and B was surprisingly 5nm so that it was possible to produce the photomask 10 with an extremelyexcellent CD characteristic.

Second Embodiment

Referring to FIG. 1, description will be made of a photomask producingmethod according to the second embodiment of this invention. In thesecond embodiment, a photomask was produced under the same condition asin the first embodiment except that the opaque chromium film 2 wasetched using only the inorganic-based etching mask pattern 31 as a maskafter removal of the resist pattern 41 in the first embodiment.

Specifically, first, a substrate made of quartz was mirror-polished andwas subjected to prescribed washing to thereby obtain alight-transmissive substrate 1 of 6 inches×6 inches×0.25 inches.

Then, by the use of an in-line sputtering apparatus where a plurality ofchromium (Cr) targets were disposed in the same chamber, an opaquechromium film 2 was formed on the light-transmissive substrate 1 (seeFIG. 1( a)).

Specifically, first, reactive sputtering was carried out in anatmosphere of mixture gas of argon (Ar) and nitrogen (N₂) (Ar:N₂=72:28[volume %], pressure 0.3 [Pa]) to thereby form a CrN film having athickness of 20 [nm].

Subsequently, reactive sputtering was carried out in an atmosphere ofmixture gas of argon (Ar) and methane (CH₄) (Ar:CH₄=96.5:3.5 [volume %],pressure 0.3 [Pa]) to thereby form a CrC film having a thickness of 37[nm] on the CrN film.

Subsequently, reactive sputtering was carried out in an atmosphere ofmixture gas of argon (Ar) and nitrogen monoxide (NO) (Ar:NO=87.5:12.5[volume %], pressure 0.3 [Pa]) to thereby form a CrON film having athickness of 15 [nm] on the CrN film.

The foregoing CrN film, CrC film, and CrON film were successively formedby the use of the in-line sputtering apparatus so that the opaquechromium film 2 containing these CrN, CrC, and CrON was configured suchthat these components continuously changed in a thickness directionthereof.

Then, by the use of a mixture target of molybdenum (Mo) and silicon (Si)(Mo:Si=20:80 [mol %]), reactive sputtering was carried out in anatmosphere of mixture gas of argon (Ar) and nitrogen (N₂) (Ar:N₂=10:90[volume %], pressure 0.3 [Pa]) to thereby form an MoSiN-basedinorganic-based etching mask film 3 having a thickness of 92 [nm] on theopaque chromium film 2 (see FIG. 1( b)).

Then, a positive electron beam resist 4 (ZEP7000: produced by ZeonCorporation) was applied on the inorganic-based etching mask film 3 tohave a thickness of 400 [nm] by the spin coat method (see FIG. 1( c)).

By the foregoing, preparation was made of a photomask blank 11 in whichthe opaque chromium film 2, the MoSiN-based inorganic-based etching maskfilm 3, and the resist 4 were formed in order on the light-transmissivesubstrate 1.

Then, the resist 4 was subjected to electron-beam drawing by the use ofJBX9000 produced by JEOL Ltd. and was then developed to thereby form aresist pattern 41 (0.4 μm line and space) as shown in FIG. 2 (see FIG.1( d)).

The formed resist pattern 41 has in the plane thereof a portion A and aportion B formed by the same pattern. In a region with a prescribed areaincluding the portion A, the resist around the portion A is not removedbut remains on the surface, while, in a region (white portion in thefigure) with the same prescribed area including the portion B, theresist around the portion B is removed so that the inorganic-basedetching mask film 3 appears on the surface. That is, by comparingpatterns at the portions A and B, it is possible to evaluate a CDcharacteristic obtained when pattern regions having a global openingratio difference are compositely present in the plane of a mask.

Then, dimensions of the obtained resist pattern 41 were measured at theportions A and B, respectively, by the use of CD-SEM (EMU-220) producedby Holon Inc.

Then, using the resist pattern 41 as a mask, dry etching mainly withionicity was carried out under a pressure of 5 [mmTorr] by the use of amixture gas of SF₆ and He to etch the inorganic-based etching mask film3 to thereby form an inorganic-based etching mask pattern 31 (see FIG.1( e)).

Then, the resist pattern 41 was removed. Thereafter, using only theinorganic-based etching mask pattern 31 as a mask, dry etching mainlywith radicals where ionicity was increased as much as possible(=ionicity was increased to a level where ions and radicals becameapproximately equal to each other) was carried out under a pressure of 3mmTorr by the use of a mixture gas of Cl₂ and O₂ to etch the opaquechromium film 2 to thereby form an opaque chromium pattern 21 (see FIG.1( f)).

Then, the inorganic-based etching mask pattern 31 was stripped, andthereafter, prescribed washing was carried out to obtain a photomask 10(see FIG. 1( g)).

Then, like the resist pattern 41, dimensions of the obtained opaquechromium pattern 21 were measured at the portions A and B, respectively,by the use of CD-SEM. As a result, a difference between size conversiondifferences (size differences each between the resist pattern 41 and theopaque chromium pattern 21) in the portions A and B was quitesurprisingly 1 nm so that it was possible to produce the photomask 10with an extremely excellent CD characteristic.

First Comparative Example

The first comparative example is a method that produces a photomaskwithout forming the inorganic-based etching mask film 3 in the photomaskproducing method according to the first embodiment.

First, a substrate made of quartz was mirror-polished and was subjectedto prescribed washing to thereby obtain a light-transmissive substrate 1of 6 inches×6 inches×0.25 inches.

Then, according to the same method as in the first embodiment, an opaquechromium film 2 comprised of a CrN film, a CrC film, and a CrON film wasformed on the light-transmissive substrate 1 by the use of an in-linesputtering apparatus where a plurality of chromium (Cr) targets weredisposed in the same chamber.

Then, a resist 4 was applied on the opaque chromium film 2 to athickness of 400 [nm] by the spin coat method like in the firstembodiment.

Then, the resist 4 was subjected to electron-beam drawing like in thefirst embodiment and was then developed to thereby form a resist pattern41 (0.4 μm line and space) as shown in FIG. 2 like in the firstembodiment. Then, dimensions of the obtained resist pattern 41 weremeasured at portions A and B, respectively, by the use of CD-SEM.

Then, using the resist pattern 41 as a mask, conventional dry etchingwith low ionicity was carried out under a pressure of 8 mmTorr by theuse of a mixture gas of Cl₂ and O₂ to etch the opaque chromium film 2 tothereby form an opaque chromium pattern 21.

Then, like in the first embodiment, the resist pattern 41 was stripped,and thereafter, prescribed washing was carried out to obtain a photomask10.

Then, like the resist pattern 41, dimensions of the obtained opaquechromium pattern 21 were measured at the portions A and B, respectively,by the use of CD-SEM. As a result, a difference between size conversiondifferences (size differences each between the resist pattern 41 and theopaque chromium pattern 21) in the portions A and B was 30 nm.Therefore, the CD characteristic was extremely inferior as compared tothe first embodiment wherein the photomask was produced by forming theinorganic-based etching mask film 3.

In the second embodiment of this invention, as compared to the firstcomparative example (conventional example), the loading effect could beremarkably suppressed and the photomask 10 could be produced with theextremely excellent CD characteristic of 1 nm which was not imaginableconventionally.

Third Embodiment

Referring to FIG. 3, description will be made of a photomask producingmethod according to the third embodiment of this invention.

First, a substrate made of quartz was mirror-polished and was subjectedto prescribed washing to thereby obtain a light-transmissive substrate 1of 6 inches×6 inches×0.25 inches.

Then, by the use of a mixture target of molybdenum (Mo) and silicon (Si)(Mo:Si=20:80 [mol %]), reactive sputtering was carried out in anatmosphere of mixture gas of argon (Ar) and nitrogen (N₂) (Ar:N₂=10:90[volume %], pressure 0.3 [Pa]) to thereby form an MoSiN-basedlight-semitransmissive phase shift film 5 having a thickness of 100 [nm]on the light-transmissive substrate 1 (FIG. 3( a)).

Then, by the use of an in-line sputtering apparatus where a plurality ofchromium (Cr) targets were disposed in the same chamber, an opaquechromium film 2 comprised of a CrN film, a CrC film, and a CrON film wasformed on the phase shift film 5 according to the same method as in thefirst embodiment (FIG. 3( b)).

Then, an MoSiN-based inorganic-based etching mask film 3 having athickness of 92 [nm] was formed on the opaque chromium film 2 accordingto the same method as in the first embodiment (FIG. 3( c)).

Then, a resist 4 was applied on the inorganic-based etching mask film 3to a thickness of 400 [nm] by the spin coat method like in the firstembodiment (FIG. 3( d)).

By the foregoing, preparation was made of a mask blank 11 of a halftonephase shift type (halftone phase shift mask blank) in which thelight-semitransmissive phase shift film 5 made of an MoSiN-basedmaterial, the opaque chromium film 2 made of a Cr-based material, theinorganic-based etching mask film 3 made of an MoSiN-based material, andthe resist 4 were formed in order on the light-transmissive substrate 1(FIG. 3( d)).

Then, like in the first embodiment, the resist 4 was subjected toelectron-beam drawing and was then developed to thereby form a resistpattern 41 (0.4 μm line and space) as shown in FIG. 2, and dimensions ofthe obtained resist pattern 41 were measured at the portions A and B,respectively, by the use of CD-SEM (FIG. 3( e)).

Then, according to the same method as in the first embodiment, dryetching of the inorganic-based etching mask film 3 was carried out usingthe resist pattern 41 as a mask to thereby form an inorganic-basedetching mask pattern 31 (FIG. 3( f)).

Then, according to the same method as in the first embodiment, dryetching of the opaque chromium film 2 was carried out using the resistpattern 41 and the inorganic-based etching mask pattern 31 as masks tothereby form an opaque chromium pattern 21 (FIG. 3( g)).

Then, using the resist pattern 41, the inorganic-based etching maskpattern 31, and the opaque chromium pattern 21 as masks, dry etching ofthe phase shift film 5 was carried out under a pressure of 5 mmTorr bythe use of a mixture gas of SF₆ and He to thereby form a phase shiftpattern 51 (FIG. 3( h)). In this event, the MoSiN-based inorganic-basedetching mask pattern 31 is etched at its portions where the resist isretreated due to the dry etching of the phase shift film 5. However,until completely etched, the inorganic-based etching mask patternprotects the opaque chromium pattern from the dry etching of the phaseshift film 5, and therefore, generation of dust caused by damage of theopaque chromium pattern due to the dry etching of the phase shift film 5can be reduced to a level that causes no influence.

Then, the resist pattern 41 and the inorganic-based etching mask pattern31 were stripped, and then the opaque chromium pattern 21 around atransfer pattern region was stripped (the opaque chromium pattern may beleft at its portions that are located in the transfer pattern region andthat are better to remain in terms of an exposure process which uses thephotomask). Thereafter, prescribed washing was carried out to obtain aphotomask 10 of a halftone phase shift type (halftone phase shift mask)(FIG. 3( i)).

Then, like the resist pattern 41, dimensions of the obtained phase shiftpattern 51 were measured at the portions A and B, respectively, by theuse of CD-SEM. As a result, a difference between size conversiondifferences (size differences each between the resist pattern 41 and thephase shift pattern 51) in the portions A and B was surprisingly 4 nm sothat it was possible to produce the halftone phase shift mask with anextremely excellent CD characteristic.

Fourth Embodiment

Referring to FIG. 3, description will be made of a photomask producingmethod according to the fourth embodiment of this invention. In thefourth embodiment, a photomask was produced under the same condition asin the third embodiment except that the opaque chromium film 2 wasetched using only the inorganic-based etching mask pattern 31 as a maskafter removal of the resist pattern 41 in the third embodiment.

Specifically, first, a substrate made of quartz was mirror-polished andwas subjected to prescribed washing to thereby obtain alight-transmissive substrate 1 of 6 inches×6 inches×0.25 inches.

Then, by the use of a mixture target of molybdenum (Mo) and silicon (Si)(Mo:Si=20:80 [mol %]), reactive sputtering was carried out in anatmosphere of mixture gas of argon (Ar) and nitrogen (N₂) (Ar:N₂=10:90[volume %], pressure 0.3 [Pa]) to thereby form an MoSiN-basedlight-semitransmissive phase shift film 5 having a thickness of 100 [nm]on the light-transmissive substrate 1 (FIG. 3( a)).

Then, by the use of an in-line sputtering apparatus where a plurality ofchromium (Cr) targets were disposed in the same chamber, an opaquechromium film 2 comprised of a CrN film, a CrC film, and a CrON film wasformed on the phase shift film 5 according to the same method as in thefirst embodiment (FIG. 3( b)).

Then, an MoSiN-based inorganic-based etching mask film 3 having athickness of 92 [nm] was formed on the opaque chromium film 2 accordingto the same method as in the first embodiment (FIG. 3( c)).

Then, a resist 4 was applied on the inorganic-based etching mask film 3to a thickness of 400 [nm] by the spin coat method like in the firstembodiment (FIG. 3( d)).

By the foregoing, preparation was made of a mask blank 11 of a halftonephase shift type (halftone phase shift mask blank) in which thelight-semitransmissive phase shift film 5 made of an MoSiN-basedmaterial, the opaque chromium film 2 made of a Cr-based material, theinorganic-based etching mask film 3 made of an MoSiN-based material, andthe resist 4 were formed in order on the light-transmissive substrate 1(FIG. 3( d)).

Then, like in the first embodiment, the resist 4 was subjected toelectron-beam drawing and was then developed to thereby form a resistpattern 41 (0.4 μm line and space) as shown in FIG. 2, and dimensions ofthe obtained resist pattern 41 were measured at the portions A and B,respectively, by the use of CD-SEM (FIG. 3( e)).

Then, according to the same method as in the first embodiment, dryetching of the inorganic-based etching mask film 3 was carried out usingthe resist pattern 41 as a mask to thereby form an inorganic-basedetching mask pattern 31 (FIG. 3( f)).

Then, according to the same method as in the second embodiment, afterremoval of the resist pattern 41, dry etching of the opaque chromiumfilm 2 was carried out using only the inorganic-based etching maskpattern 31 as a mask to thereby form an opaque chromium pattern 21 (FIG.3( g)).

Then, using the resist pattern 41, the inorganic-based etching maskpattern 31, and the opaque chromium pattern 21 as masks, dry etching ofthe phase shift film 5 was carried out under a pressure of 5 mmTorr bythe use of a mixture gas of SF₆ and He to thereby form a phase shiftpattern 51 (FIG. 3( h)).

Then, using the resist pattern 41, the inorganic-based etching maskpattern 31, and the opaque chromium pattern 21 as masks, dry etching ofthe phase shift film 5 was carried out under a pressure of 5 mmTorr bythe use of a mixture gas of SF₆ and He to thereby form a phase shiftpattern 51 (FIG. 3( h)). In this event, the MoSiN-based inorganic-basedetching mask pattern 31 is etched due to the dry etching of the phaseshift film 5. However, until completely etched, the inorganic-basedetching mask pattern protects the opaque chromium pattern from the dryetching of the phase shift film 5, and therefore, generation of dustcaused by damage of the opaque chromium pattern due to the dry etchingof the phase shift film 5 can be reduced to a level that causes noinfluence.

Then, the resist pattern 41 and the inorganic-based etching mask pattern31 were stripped, and then the opaque chromium pattern 21 around atransfer pattern region was stripped (the opaque chromium pattern may beleft at its portions that are located in the transfer pattern region andthat are better to remain in terms of an exposure process which uses thephotomask). Thereafter, prescribed washing was carried out to obtain aphotomask 10 of a halftone phase shift type (halftone phase shift mask)(FIG. 3( i)).

Then, like the resist pattern 41, dimensions of the obtained phase shiftpattern 51 were measured at the portions A and B, respectively, by theuse of CD-SEM. As a result, a difference between size conversiondifferences (size differences each between the resist pattern 41 and thephase shift pattern 51) in the portions A and B was quite surprisingly 2nm so that it was possible to produce the halftone phase shift mask withan extremely excellent CD characteristic.

Second Comparative Example

The second comparative example is a method that produces a photomaskwithout forming the inorganic-based etching mask film 3 in the photomaskproducing method according to the third embodiment.

First, a substrate made of quartz was mirror-polished and was subjectedto prescribed washing to thereby obtain a light-transmissive substrate 1of 6 inches×6 inches×0.25 inches.

Then, like in the second embodiment, an MoSiN-basedlight-semitransmissive phase shift film 5 having a thickness of 100 [nm]was formed on the light-transmissive substrate 1.

Then, according to the same method as in the second embodiment, anopaque chromium film 2 comprised of a CrN film, a CrC film, and a CrONfilm was formed on the phase shift film 5 by the use of an in-linesputtering apparatus where a plurality of chromium (Cr) targets weredisposed in the same chamber.

Then, a resist 4 was applied on the opaque chromium film 3 to athickness of 400 [nm] by the spin coat method like in the secondembodiment.

Then, like in the second embodiment, the resist 4 was subjected toelectron-beam drawing and was then developed to thereby form a resistpattern 41 (0.4 μm line and space) as shown in FIG. 2, and dimensions ofthe obtained resist pattern 41 were measured at portions A and B,respectively, by the use of CD-SEM.

Then, according to the same method as in the first comparative example,dry etching of the opaque chromium film 2 was carried out using theresist pattern 41 as a mask to thereby form an opaque chromium pattern21.

Then, using the resist pattern 41 and the opaque chromium pattern 21 asmasks, dry etching was carried out like in the second embodiment tothereby form a phase shift pattern 51.

Then, the resist pattern 41 was stripped, and subsequently, the opaquechromium pattern 21 around a transfer pattern region was stripped.Thereafter, prescribed washing was carried out to obtain a photomask 10of a halftone phase shift type.

Then, like the resist pattern 41, dimensions of the obtained phase shiftpattern 51 were measured at the portions A and B, respectively, by theuse of CD-SEM. As a result, a difference between size conversiondifferences in the portions A and B was 35 nm. Therefore, the CDcharacteristic was extremely inferior as compared to the secondembodiment wherein the photomask was produced by forming theinorganic-based etching mask film 3.

Fifth Embodiment

Now, description will be made of a chromeless-type phase shift maskproducing method according to the fifth embodiment of this invention.

The fifth embodiment is an example wherein a chromeless-type phase shiftmask was produced by further etching the substrate using the opaquechromium film pattern as a mask from the state before the stripping ofthe inorganic-based etching mask in the second embodiment.

First, a photomask before stripping of an inorganic-based etching maskwas produced according to the same method as in the second embodiment.

Then, using as a mask an opaque chromium pattern 21 with aninorganic-based etching mask pattern 31 in the photomask 10, a substratewas etched to a thickness of 180 nm where the phase difference becameabout 180°. This etching was carried out under a pressure of 0.3 Pausing a mixture gas of Cl₂, O₂, and He as a dry etching gas. In thisevent, the MoSiN-based inorganic-based etching mask pattern 31 is etcheddue to the dry etching of the substrate. However, until completelyetched, the inorganic-based etching mask pattern protects the opaquechromium pattern from the dry etching of the substrate, and therefore,generation of dust caused by damage of the opaque chromium pattern dueto the dry etching of the substrate can be reduced to a level thatcauses no influence.

Then, the opaque chromium pattern was stripped such that an opaquechromium film at least around a transfer region was left (the opaquechromium pattern may be left at its portions that are located in thetransfer pattern region and that are better to remain in terms of anexposure process which uses the photomask). Thereafter, prescribedwashing was carried out to obtain a chromeless-type phase shift mask.

According to the obtained chromeless-type phase shift mask, the CDcharacteristic of the opaque chromium pattern 21 of the photomask 10 istransferred so that it is possible to produce the chromeless-type phaseshift mask having an extremely excellent CD characteristic.

Further, according to this embodiment, the inorganic-based etching maskis simultaneously etched in the etching of the substrate, and therefore,the process of stripping the inorganic-based etching mask is notrequired.

In this embodiment, if a material and a thickness of the inorganic-basedetching mask pattern are selected such that the etching of the substrateand the etching of the inorganic-based etching mask pattern are finishedin the same etching time, it is preferable in that it becomes possibleto detect the termination point of the etching of the substrate bydetecting the termination point of the etching of the inorganic-basedetching mask pattern.

Third Comparative Example

The third comparative example is an example wherein a chromeless-typephase shift mask was produced by further etching the substrate using theopaque chromium film pattern as a mask from the state before thestripping of the inorganic-based etching mask in the first comparativeexample.

First, a photomask before stripping of an inorganic-based etching maskwas produced according to the same method as in the second comparativeexample.

Then, using as a mask an opaque chromium pattern 21 in this photomask, asubstrate was etched to a thickness of 180 nm where the phase differencebecame about 180°. This etching was carried out under a pressure of 0.68Pa using a mixture gas of CF₄ and O₂ as a dry etching gas. In thisevent, it was confirmed that surfaces of etched portions of thesubstrate were roughened under the influence of generation of dustcaused by damage of the opaque chromium pattern due to the dry etchingof the substrate.

Then, the opaque chromium pattern was stripped such that an opaquechromium film at least around a transfer region was left (the opaquechromium pattern may be left at its portions that are located in thetransfer pattern region and that are better to remain in terms of anexposure process which uses the photomask). Thereafter, prescribedwashing was carried out to obtain a chromeless-type phase shift mask.

According to the obtained chromeless-type phase shift mask, the CDcharacteristic was extremely inferior as compared to the fifthembodiment.

In the first to fifth embodiments of this invention, use is made of themixture gas of SF₆ and He in the dry etching mainly with ions. However,by setting a proper dry etching condition, a similar effect can beachieved using a gas such as CF₄, C₂F₆, or CHF₃, or a mixture gasthereof with He, H₂, N₂, Ar, C₂H₄, or O₂.

Further, in the first to fifth embodiments of this invention, use ismade of the MoSiN-based material for the inorganic-based etching maskfilm. However, a similar effect can be achieved using Mo alone, MoSi,MoSiO, MoSiN, MoSiON, Si alone, SiO, SiN, SiON, Ta alone, TaB, W, WSi,or TaSi.

Further, in the first to fifth embodiments of this invention, use ismade of the mixture gas of Cl₂ and O₂ in the dry etching mainly withradicals. However, by setting a proper dry etching condition, a similareffect can be achieved using a mixture gas of CH₂Cl₂ and O₂, or amixture gas thereof with He, H₂, N₂, Ar, or C₂H₄.

As described above, according to this invention, it is possible tosuppress the loading effect and to achieve a high CD accuracy whenforming a highly accurate pattern by dry etching, in a photomask havinga global opening ratio difference (variation in CD accuracy due to theloading effect becomes a problem).

It is possible to form a pattern having a high CD accuracy regardless ofthe foregoing regions (over the whole surface of the mask) having aglobal opening ratio difference (variation in CD accuracy due to theloading effect becomes a problem) in the mask plane.

Further, this invention can suppress the loading effect and achieve ahigh CD accuracy in etching an opaque chromium film as an etching maskfilm when producing a halftone-type phase shift mask or achromeless-type phase shift mask comprising a phase shift layer having aglobal opening ratio difference (variation in CD accuracy due to theloading effect becomes a problem).

1. A photomask blank serving as a base member for producing a halftone-type phase shift mask in which a light-transmissive substrate is formed thereon with a light-semitransmissive phase shift pattern having a desired opening, said photomask blank characterized in that a light-semitransmissive phase shift film, a chromium film, and an etching mask film made of an inorganic-based material having a resistance against dry etching of said chromium film are stacked in order on said light-transmissive substrate.
 2. A photomask blank according to claim 1, characterized in that said light-semitransmissive phase shift film comprises an uppermost layer made of a material containing silicon, and nitrogen and/or oxygen.
 3. A photomask blank according to claim 2, characterized in that said light-semitransmissive phase shift film is a film of a monolayer structure made of a material containing metal, silicon, and nitrogen and/or oxygen.
 4. A photomask blank according to claim 1, characterized in that said etching mask film is made of a material that is possible to strip with the dry etching of said light-semitransmissive phase shift film.
 5. A photomask blank according to claim 1, characterized in that said etching mask film is a film having a reflection preventing function.
 6. A photomask blank according to claim 4, characterized in that said etching mask film is made of a material containing silicon, nitrogen and/or oxygen.
 7. A photomask blank according to claim 6, characterized in that said etching mask film is made of a material selected from the group consisting of MoSiO, MoSiN, MoSiON, SiO, SiN, and SiON.
 8. A photomask blank according to claim 1, characterized by further comprises a resist film formed on said etching mask film.
 9. A photomask blank according to claim 1, characterized in that a dry etching rate of said chromium film is ten or more times an etching rate of said etching mask film.
 10. A photomask blank according to claim 8, characterized in that selection ratio of etching rate of said etching mask film/etching rate of said resist film is two or more.
 11. A photomask blank according to claim 1, characterized in that said etching mask film has a thickness between 5 nm and 30 nm.
 12. A halftone-type phase shift mask in which said light-semitransmissive phase shift pattern is formed on said light-transmissive substrate by patterning said light-semitransmissive phase film in said photomask blank according to claim
 1. 13. A halftone-type phase shift mask according to claim 12, characterized in that said halftone-type phase shift mask is for use in production of a system LSI, a D-RAM, or a liquid crystal display device. 